Telephone transmitter with radial slots in the carbon chamber



Oct. 24, 1950 R. R. STEVENS 2,527,159V

TELEPHONE TRANSMITTER WITH RADIAL sLoTs IN TRE CARBON CHAMBER FiledApril 26, 1947 2 Shee-ts-Shee-t-I ATTORNEY Ot. 24, 1950 R. R. STEVENSTELEPHONE TRANSMITTER WITH RADIAL SLOTS IN THE CARBON CHAMBER FiledApril 26, 1947 2 Sheets-Sheet 2 lllllllllil'l /NVENTOR By R. R. STEVENS7`7'R/VEV Patented Oct. 24, 1950 TELEPHONE TRANSMITTER WITH 'RADIAL-SLOTS IN THE CARBON CHAMBER Ralph R. Stevens, Chatham, N. J., assignorto Bell' Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York,u

Application April 26, 1947, seriaiNo. 744,059 f This invention relatesto telephone transmitters and more particularly to carbon granuletransmitter units especially suitable for use in hand telephones.

Such transmitter units, of which the unit disclosed in Patent 2,042,822,granted June 2, 1936 to Arthur L. Bennett and William L. Tuffnell isillustrative, comprise in general a iixed and a movable electrodeassociated with a chamber containing carbon granules to define avariable re-V sistance path; Operating desiderata for the units includehigh modulation efficiency and non-positional response characteristics,i. e., freedomof variation in the operating characteristics with changesin position in which the units are held during use thereof.Additionally, it is' eminently desirable in some elds of use that theresistance of the units be relatively high. y

It has been found that, generally speaking, carbon granules of suchcharacter that good modulation efliciency is obtained by their use havea relatively low resistance.

One object of this invention is to obtain a relatively high resistancefor transmitter units of the carbon granule type.

More specifically, one object of the invention is to increase theresistance of such transmitter units without degradation of either themodulation efficiency or non-positional operating characteristicsthereof.

Another object of this invention is to enable ready collocation of theelements defining the carbon granules chamber in a transmitter inprescribed relation, specifically in accurate coaxial relation, wherebythe manufacture of units is facilitated and realization of uniformity ofproduct in quantity manufacture is expedited.

In accordance with one feature of this invention, in a carbon granuletype transmitter having juxtaposed fixed and vibratile electrodesurfaces, an insulating insert is provided between the surfaces forreducing the effective cross-sectional area of the current path betweenthe two electrodes whereby the transmitter resistance is substantiallyincreased.

More specifically, in accordance with one feature of this invention, theinsert is fitted against the dished surface of the fixed electrode andis constructed and arranged to divide a portion of the granule chamberinto a plurality of slots extending radially from a central spacecoaxial with the electrode surfaces, whereby a plurality ofsubstantially identical current paths electrically in parallel areprovided between the e160- trodes.

14 Claims. (Cl. 179-122) ill) In accordance withanother feature ofthis'lnivention, the electrodes and other elements bounding the carbongranule chamber are mounted by a support or foundation member and arephysically associated therewith and with one another in such manner thatlthe electrodes and elements are accurately positioned in coaxialrelation automatically upon placement thereof inor onto thefoundation'member 'in the assembly of the unit.

The invention and thevabove-noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the :accompanying drawing in y which:

Fig. 1 is a side elevational view of a transmitter unit illustrative ofoneembodiment of this invention;

Fig. 2 is a diametral sectional View of the transmitter unit sh'owrifinFig. 1;` I f Fig. 3 isa plan view of the insulating insert included inthe unit; 'f

Fig.` 4 is a partial view in section of a transmitter unit illustrativeof y'another embodiment of this invention; and Fig. 5 isavfaceview ofthe damping plate included in the transmitter unit illustrated in Fig.4. v

Referring now to -thedrawing the transmitter unit shown in Figs-l and 2is adapted for use particularly in hand telephones such as disclosed inthe application, Serial No. 744,179 led April 26, 1947 of William G.Turnbull and comprises a circular metallic frame or foundation member,designated generally as I0,`liaving a shallow cylindrical portion II',an annular inwardly extending flange I2 and a secondcylindrical portionI3 co-f axial with the 4portion II and terminating in an outwardlydirected flange I4.

A diaphragm, for example formed in one piece of a lightweight metal-suchas duralumin, corn'V prises af'central frusto-conical portion I5provided with radially extending stilfening 'utes or corrugations I6, anannular peripheral portion I'I and an intermediate, annular troughportion or corrugation I8. The annular portion I'I is seated upon theend ofthe cylindrical part I I of the foundation member; the corrugationI8 abuts the cylindrical portion 'I I` and'is sufficiently flexible toallow bodily'mov'ement, analogous to a piston, of the frusto-conicaldiaphragm portion I 5.

' Disposed in frontv of the diaphragm is a moisture-proof membrane I9over or in front of ywhich a metallic, multi-apertured protective grillor cap 20 extends. The membraney I 9,-grill or caprZD and peripheralportion I1 of the diaphragm together with a washerfzl; are securedtogether-l and against the end of the frame or foundation member by aclamping band 22 having a flange 23 bearing against the washer 2| andhaving one end crimped over the frame as illustrated at 24.

An electrode, for example of brass, mounted on the frusto-conicaldiaphragm portion I5, is vibratile therewith and comprises ahemispherical portion 25 and a circular cylindrical part 26. The latteris provided with an annular flange 21 having integral tabs 28, theflange and tabs being adjacent opposite faces of an annular flange 29 onthe diaphragm and locking the electrode thereto. The outer surface ofthe electrode may be plated with a low resistance material such as, forexample, gold.

Arranged in pile-up fashion upon the flange I2 are a metallic spacerring 30, an annular insulator 3|, a metallic back electrode 32, and aninsulating insert 33, the ring 30 being insulated Y from the frame l 0by a thin cup-shaped insulating member 34. The insulator 3l has anupstanding cylindrical flange 50 coaxial with the electrode 25, 26against which the periphery of the insert 3| is fitted, whereby theinsert is llocated in coaxial relation with the electrode 25,

26. The back electrode 32 includes a central rdished portion 35 theinner surface of which is hemispherical and coaxial with but eccentricwith respect to the portion 25 of the movable electrode.

The insulating insert 33, which in a particularly advantageousconstruction is of anodized aluminum, includes a central portioncomprising a plurality of radially extending, inwardly Itapered arms orsections'.y 36 which are equally spacedl to form a plurality of radialslots 31, as shown clearly in Fig. 3, extending from a centralcylindrical opening 38. As shown in Fig. 2, the arms or sections 36 aregenerally arcuate and the curved walls thereof conform to segments ofhemispherical surfaces coaxial with but eccentric with respect to thehemispherical portion 25 of the movable electrode. The outer walls ofthe arms conform to and t against the inner surface of the dished part35 of the back electrode, whereby this electrode is located coaxiallywith the electrode portion 25.

Clamped at one margin between the ring 30 and insulator 3| and at itsother margin between the flanges 21 and 29 is aA thin, flexibleinsulating annulus 39, for example of silk. This annulus, together withthe front and back electrodes, the insert 33 and insulator 3|, denes achamber which is lled with carbon granules. In the interest of clarityof illustration, the carbon granule lling is not shown in Fig. 2. Thecarbon granules are introduced into the chamber through the outer end ofthe back electrode and the opening in this end is closed subsequently bya, metallic cap 40 crimped over this electrode and adapted to serve as aterminal or contact through which electrical connection to the backelectrode may be established.

Electrical connection to the front electrode 25, 26 is established by athin, metallic spider member having a plurality of bent, flexible arms4|. These arms extend radially from an integral annulus clamped betweenthe diaphragm flange 29 and annulus 39 and have their cuter ends clampedbetween the flange |2 and the insulating member 34.

The elements arranged in pile-up fashion upon the flange I2 of the frameor foundation member |8. are locked or clamped in place in coaxialrelation by a metal ring spring 42 having a flange 43 bearing against aninsulating washer 44 and having its outer marginal part crimped underthe ange |4 as indicated at 45. As shown clearly in Fig. 2, the washer44 fits slidably within the cylindrical portion |3 of the frame orfoundation member |0.

It will be noted that the insulating insert 33 not only reduces theeffective cross-sectional area of the current path between the movableelectrode 25 and 26 but also assures a relatively long current path.Hence, a relatively high resistance, for example of the order of 45ohms, is realized for the transmitter unit. It has been found that theinsert does not affect deleteriously the modulation characteristics ofthe unit so that the desired high resistance is attained withoutdegradation of the modulating efficiency. Furthermore, it has been foundthat because of its construction and particularly of the plurality ofradial slots 31 extending from the central space 38, the transmitterunit is highly non-positional. Thus, the desiderata of high resistance,good modulation and non-positional characteristics are realized intransmitter units constructed in accordance with this invention.Additionally, it has been found that the insert reduces the tendency ofthe carbon granules to pack to an insensitive state.

It will be noted further that the various elements bounding the granulechamber are aligned in accurate coaxial relation by mere assembly of theparts. Specifically, the diaphragm and the movable electrode arepositioned in coaxial relation with the frame l0 by edge abutment of theannular corrugation I8 with the cylindrical part of the frame; theinsulating ring 3| automatically is located coaxially with the electrode25, |6 when the ring is inserted into the cupshaped member 34 and, inturn, by virtue of engagement of the flange with the periphery thereof,locates the insert 33 in coaxial relation with the electrode 25, 26; andthe insert positions the back electrode 35 coaxially with respect to theother elements. Hence, the construction facilitates the manufacture ofhigh quality transmitter units and enables manufacture of such units inquantity at low cost.

Because of its mass and stiffness, the diaphragm may have a vibrationalresonance frequency within the intended operating range of thetransmitter unit, which would result in distortion of the transmittedsignals. To prevent such distortion, there is provided in associationwith the diaphragm an acoustic network for damping the diaphragm tosubstantially suppress the response peak clue to the resonance and forequalizing the response over a broad frequency band. This network isconstituted by the chamber 45V behind the diaphragm and a plurality ofapertures 41 in the frame over which acoustic resistance material 43,such as acoustic silk, extends, the chamber 46 providing the stiffnesscomponent of the network and the material 48 the mass and resistancecomponents thereof.

In another illustrative construction, shown in Figs. 4 and 5, the frameor foundation member comprises two mating parts IDA and IDB, the partIGB being provided with shallow radially extending slots 49 which extendfrom the chamber 46 to the apertures 41 and provide the mass andresistance components of the damping network.

Although specific embodiments of the invention have been shown anddescribed, it; will be understood that they vare but'illu'str'ative andthat various modications may be made therein y without departing fromthe scope and-spirit of thisv invention as defined in the appendedclaims. What is claimed is: v f v l'. A telephone transmittercomprising-means including a pair of juxtaposed electrodesbounding acarbon granule chamber, one of said electrodes being vibratile to varythe current path between said electrodes, and insulating means in SaidAchamber dividing a portion of said current path'into a central part anda plurality of yseparate partsextending outwardly from said central partto o-ne of said electrodes.

2. A telephone transmitter comprising means including a pair of opposed,axially aligned electrodes bounding a carbon granule chamber, one ofsaid electrodes being vibratile to vary the current path between saidelectrodes, and insulating means within said chamber dividing a portionof the space between said electrodes into a central cylindrical partcoaxial with said electrodes and a plurality of parts extending radiallyfrom said central part.

3. A telephone transmitter comprising means including a pair ofelectrodes bounding a carbon granule chamber, one of said electrodeshaving a dished portion in juxtaposition to the other electrode, and aninsulating insert in said portion, said insert having a central openingtherein and having also a plurality of arms defining a plurality ofslots extending from said opening to said one electrode.

4. A telephone transmitter comprising means including a pair ofelectrodes bounding a carbon granule chamber, one of said electrodesbeing vibratile and said electrodes having juxtaposed axially alignedportions dished in the same direction, and an insulating insert tted inone of said portions and dividing the space therein into a plurality ofslots extending radially with respect to the axis of alignment of saidportions.

5. A telephone transmitter comprising means including a pair ofelectrodes bounding a carbon granule chamber, one of said electrodesbeing xed and having a concave portion and the other of said electrodesbeing vibratile and having a convex portion `in juxtaposition to saidconcave portion, and an insulating insert in said concave portion,fitted in face to face relation therewith and having therein a pluralityof slots dening separate current paths between said concave and convexportions.

6. A telephone transmitter comprising means including a pair ofelectrodes bounding a carbon granule chamber, one of said electrodesbeing xed and having a concave portion and the other of said electrodesbeing vibratile and having a convex portion in juxtaposition to saidconcave portion, and insulating means intermediate said convex andconcave portions dividing a portion of the space therebetween into aplurality of similar slots extending from said concave portion.

'7. A telephone transmitter comprising a xed electrode having a concavesurface, a vibratile electrode having a convex surface opposite and.

axially aligned with said concave surface, means including said fixedand vibratile electrodes bounding a carbon granule chamber, and aninsulating member within and in face to face relation with said concavesurface and having a plurality of arms extending radially inwardly fromsaid concave surface.

6,. *8; A telephone transmitter in accordance with' claim7 Wherein'saidarms taper inwardly `'from saidconcave surface. f y

9; A telephone `transmitter in accordancewith claim 7-wherein each ofsaid arms has one vedge faceliittedvto said concave surface and theopposite edge face in juxtaposition to andfcurved inthe samefdirectionas said convex face.

10. A telephone transmitter comprising a first electrode having a dishedportion, a vibratile electrode; having a convex surface opposite saiddished portion, means including said first and vibratile electrodesbounding a carbon granule chamber, and an insulating insert in saiddished portion including a plurality of arms having faces toward saidconvex surface lying in a concave boundary coaxial with and eccentricwith respect to said convex surface.

11. A telephone transmitter comprising a first electrode having aconcave substantially hemispherical surface, a vibratile electrodehaving a convex substantially hemispherical surface opposite, axiallyaligned with and eccentric with respect to said concave surface, meansincluding said concave and convex surfaces bounding a carbon granulechamber, and an insulating insert in said rst electrode including aportion having a convex face tted to said concave surface and a concavepart in juxtaposition to, coaxial with and eccentric with respect tosaid convex surface, said portion having an axial opening therethroughand having also a plurality of arms denning slots extending radiallyfrom said opening to said concave surface.

l2. A telephone transmitter in accordance with claim 11 wherein saidarms taper inwardly from said concave surface to said opening.

13. A telephone transmitter comprising a foundation member having acylindrical portion and an annular flange extending inwardly adjacentone end of said portion, a diaphragm mounted on said member, a firstelectrode coupled to said diaphragm and coaxial with said portion, andmeans mounted upon said flange and dening a lcarbon granule chamber withsaid electrode, said means including an annular member supported fromsaid flange, positioned coaxially with said electrode by saidcylindrical portion and having a flange coaxial with said electrode, asecond electrode, and a second annular member between said secondelectrode and said rst annular member, said second annular member beingseated upon said rst annular member and positioned in coaxial relationtherewith by said coaxial ange and said second electrode being seatedupon said second annular member and positioned in coaxial relationtherewith by said second annular member.

14. A telephone transmitter comprising a foundation member having acylindrical portion and an inwardly extending flange adjacent one end ofsaid cylindrical portion, a diaphragm mounted upon said member, anelectrode coupled to said diaphragm, coaxial with said cylindricalportion and extending into said cylindrical portion at said one endthereof, and means comprising a pile-up of elements upon said angedening a carbon granule chamber with said electrode, said elementsincluding an annular insulating member supported from said flange andpositioned in coaxial relation with said electrode by said cylindricallportion, said insulating member having an upstanding cylindrical flangecoaxial therewith, a second electrode having an outer flange and acentral dished portion the concave face of which 7 is toward said rstelectrode, and Van insulating insert between said second electrode andsaid insulating member, said insert having an :annular flange seatedupon said insulating member and coaxially fitted within said upstandingcylindrical flange and having `also a -central coaxial portion fitted tosaid concave face.

RALPH R. STEVENS.

REFERENCES CITED Number Number 8 UNITED STATES PATENTS Name Date ComerJuly 28, 1914 Smith Oct. 27, 1925 Moore Dec. 15, 1925 Bennett June 2,1936 Stevens Dec. 17, 1940 Sutton July 29, 1941 FOREIGN PATENTS CountryDate Great Britain Nov. 29, 1940

